The human polyomavirus, JCV, establishes a lifelong persistent infection and is generally not associated with disease in healthy individuals. In immunosuppressed patients reactivation and spread of JCV to the central nervous system causes a fatal demyelinating disease known as progressive multifocal leukoencephalopathy (PML). Our immediate goals are to define the structural features of the JCV surface that allow for cell binding and infection and to identify molecules that antagonize these interactions. In this project we will use structural information provided by project #1 to guide mutagenesis and testing of amino acid residues in the virus capsid that are hypothesized to interact directly with cell surfaces allowing for productive infection. We will work closely with project #3 to identify and screen compounds for their ability to antagonize these interactions. In preliminary experiments we've established that two small molecular weight human alpha defensins potently inhibit infection by JCV, BKV, and SV40 most likely by binding to a shared domain on the virion surface. Specific aim #3 of this project will focus on determining the mechanism of action of alpha defensin inhibition of JCV infection. Working together with the Pis of projects 1 and 3 we will determine the structural basis for inhibition by these molecules